Comments by Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 22 September 2017

    Hello.

    If you understand the system you are putting the battery into, you should be able to tell if anything would be affected badly. The 10 Ah battery should last about four times as long as the 2.5 Ah battery, and if you don't change anything, charging should take about four times as long. If you are putting the battery into a system you do not understand or control, things could be more complicated, depending on how smart or helpful your device is. For instance, you might be fine waiting 20 hours instead of five hours for charging, but your device might have a timeout after six hours or it might think there is a problem and stop working normally.

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 30 August 2017

    Hello, Don.

    You generally cannot force a current out of a battery and into something. If you have a load that wants to use 3A when you connect it to 12V, the battery should be capable of delivering that.

    - Jan

  • Electrical characteristics of servos and introduction to the servo control interface

    Electrical characteristics of servos and introduction to the servo control interface

    - 14 June 2017

    Hi, Gustavo.

    Your question is not clear. If you are asking about characteristics of servos, as in can you stick 1.2k in series between your RC control signal and the servo (NOT between signal and ground, which would be in parallel with the servo), it's a little more than I'm comfortable with (I would use something like 220 ohms) but should probably be fine. Things like the particular servo you have and the wiring lengths will matter, so you should try to look at the signal on the servo side with an oscilloscope to make sure it looks decent.

    If you are asking about the characteristics of receivers or other servo controllers, as in can you put a 1.2k resistor in parallel (NOT series) between signal and ground, that will depend on your receiver, and 1.2k is a little on the small side (I would use about 10k for a pull-down resistor). You can again look at the signal with an oscilloscope to see if the resistor is deforming the signal too much.

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 31 May 2017

    Hi, Kerron.

    Yes, that's right: 24V could damage a device expecting 18V, and the current part should be okay. (So you should use your device with an 18V voltage regulator, and make sure that it can comfortably take a 24V input and deliver at least the 1.67A you need.)

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 22 May 2017

    Hi.

    It looks like you either did not read the blog post or did not get the point of it. 20A is about how fast you can get the energy out, not the capacity of the cell. 3.7V and 2.2 Ah give you 8.14 Wh per cell, and that multiplied by 1234 gives you just over the 10 kWh.

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 16 May 2017

    Hi.

    A 12V adapter connected directly to the battery is unlikely to be an appropriate charger. A 12V battery showing you 9V is definitely not good and charged. I am not sure how you are measuring the 0.2amps, that will be a function of your load, and a good battery should definitely be able to supply much more than that. The voltage will gradually go down as your battery discharges. You can probably find a datasheet for the battery you are using and get more specific information. You will need to regulate to 5V anyway, so your main concern should be not discharging your battery too much. And you should get a switching regulator, which should need less than 500mA to output 1A when going from 12V to 5V.

    - Jan

  • Balboa is here!

    Balboa is here!

    - 4 April 2017

    Thanks, and thanks for sharing your robot! The most difficulty came from wanting the Balboa to be able to pop up on its own. I will write up a blog post about it once I find more old prototypes to take pictures of (this project has been going on for maybe eight years, during which we moved several times).

    - Jan

  • Servo control interface in detail

    Servo control interface in detail

    - 20 January 2017

    Kenneth,

    I don't think I implied what you seem to think I did. Did you see the post before this one?

    https://www.pololu.com/blog/16/electrical-characteristics-of-servos-and-introduction-to-the-servo-control-interface

    I think it is not helpful to classify the servo control signals as those in 72 MHz systems vs those in 2.4 GHz systems since that is just the frequency that the transmitter uses to communicate with the receiver and says nothing about what kind of signal the receiver is outputting to the servos. There can of course be differences from brand to brand and unit to unit. You should definitely just look at your particular signals with a scope.

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 3 January 2017

    Hello.

    The math stays the same. An 18 Ah battery should provide 18 A for about an hour, so it should be safe if you only need it to last half an hour.

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 18 January 2016

    Your math about how long the batteries would last is fine, but the point is you should avoid putting your battery packs in parallel. You should try to use bigger cells if you really need the 5Ah in one pack, or you could put three fans on each pack and have two parallel systems.

    If you really want a single pack of eight AA cells, you could put them all in series to make a 9.6V pack, then put pairs of fans in series and power them from the higher voltage. I don't know about the details of the fans, so this could be tricky in the same way that putting batteries in parallel is tricky: it's difficult to ensure the power will get shared evenly. For instance, if the fan is just a motor and you stall one of the series pair, the voltage across it would go to 0V and the other fan would get the full battery voltage of around 9.6V, which might damage it.

    - Jan

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